Final answer:
Archeologists know the Harappan civilization was advanced through the presence of brick architecture, sanitation systems, and grid-system roads.
Step-by-step explanation:
Archeologists know that the Harappan civilization in the Indus River valley was advanced through several pieces of evidence.
Firstly, the Harappans built architecture using bricks, such as the famous Great Bath and the well-planned city of Mohenjo-daro. The use of bricks in construction suggests advanced engineering techniques.
Secondly, the presence of sophisticated sanitation systems, including covered drains and toilets, indicates a high level of urban planning and hygiene.
Lastly, the development of a grid-system for roads demonstrates urban planning and organization.
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